2011-03-29 14:47:53Soot and global warming
John Cook


Sarah Green, a scientist from MTU, recently sent me a rebuttal to "Global warming is caused by soot" along with this message:

I hope you can use it anyhow. It's close to some arguments that you already have, but I don't see anything addressing soot directly. I was motivated by a guy jumping up at a recent presentation (not by me) and insisting that the graphic shown by the speaker was out of date since it showed CO2 instead of soot as the major driver of climate. I responded when the speaker couldn’t.

So I've added a blog post using Sarah's rebuttal:


And here's the rebuttal to "It's soot":


Feedback welcome and if anyone can come up with a clever headline, would be great (come on wordsmiths, let's see what you can do).

2011-03-29 15:11:26
Daniel Bailey
Daniel Bailey

"How Soot it is"

"Soot, the darker CO2"

"Soot is a fun date, but the marriage to CO2 is forever"

"Soot, I coulda had a V8!"

2011-03-29 22:29:41
Ari Jokimäki


FYI, few months ago a new study of black carbon in Arctic was published:

"The BC content of the Arctic atmosphere has declined markedly since 1989, according to the continuous measurements of near-surface air at Alert (Canada), Barrow (Alaska), and Ny-Ålesund (Svalbard). Correspondingly, the new BC concentrations for Arctic snow are somewhat lower than those reported by Clarke and Noone for 1983–1984, but because of methodological differences it is not clear that the differences are significant. Nevertheless, the BC content of Arctic snow appears to be no higher now than in 1984, so it is doubtful that BC in Arctic snow has contributed to the rapid decline of Arctic sea ice in recent years."


2011-03-30 03:31:42blog post comments
Dana Nuccitelli

"Black carbon is a “short-term” climate forcer. Over the short term it is an important contributor to warming;" <= it would be nice to quantify or explain this a bit.  Maybe just note that black soot immediately decreases albedo - the only lag is the time between emissions and final disposition on the ground.

"Because of its short lifetime in the atmosphere, the effects of BC are most important regionally,"

"Finally, open field burning of agricultural waste should be eliminated" <= back in grade school I did a "commercial" for a science competition about burning of rice fields in California.  Dressed up like a farmer and everything.  We've since eliminated the practice, but it just reminds me that even in a developed country we were engaged in large-scale agricultural waste burning just 15-20 years ago.

Would probably be good to define "CO" and maybe even "CO2" before their use.

As a side note, I'm glad to see us do a post on black carbon.

2011-03-30 14:32:31Thanks for the helpful feedback.
Sarah Green

Thanks for the helpful feedback.

 Ari, I've included some info from that reference. dana1981, I added the comma, and edited to address your other comments.


"Soot today, gone tomorrow"

"Soot today, CO2 tomorrow"

"Cinders in the sky"



2011-03-30 14:43:49Welcome to Skeptical Science
Daniel Bailey
Daniel Bailey

Ooh!  "Cinders in the sky", I like it!


Any chance for a visual for eye candy puposes?


For example, a quick Google search yielded these:


Black Carbon




Emission sources

2011-03-30 15:58:21
Rob Painting

Another vote for "Cinders in the sky". And thumby.

2011-03-30 16:14:28welcome
Dana Nuccitelli

Hi Sarah, welcome aboard and nice post!

2011-03-30 23:32:28
Sarah Green

Here's another image from the UNEP library:



 (image by Riccardo Pravettoni, UNEP/GRID-Arendal)

UNEP/GRID-Arendal, 'Black Carbon Emissions', UNEP/GRID-Arendal Maps and Graphics Library, 2009, <http://maps.grida.no/go/graphic/black-carbon-emissions> [Accessed 30 March 2011]

2011-03-31 05:27:00


Well done Sarah, I think SkS really needed to address black carbon directly. A few suggestions.
You should start with the health effects, not end with them. Probably this is the main concern for most of the readers.
You definitely need a graph or a map to quantify BC emissons. The one in your comment above looks good to me.
You mention the effect on rainfall but do not say anything about it's effect on the number and size of cloud condensation nuclei. A single sentence somewhere would be helpfull.

2011-03-31 12:43:14Cool UNEP infographic
John Cook


Sarah, once you're happy with the blog post/rebuttal to go live, please post here and I'll add it into the schedule. Thanks!

2011-03-31 14:46:18
Sarah Green

Hi John,

Please take one more look- I'm not too sure about how big to make the image, or how to make its reference stick to it- I just referenced it at the bottom of the page (my html is rather rusty). Else, I'm done.

Riccardo, thanks for the suggestions. I decided not to wade into the cloud condensation issue here; it's still a very active and complicated research topic. I did move health effects to the top.



2011-03-31 15:00:42Let me know if you want me to do the same with the blog post
Daniel Bailey
Daniel Bailey

I took the liberty of tweaking the rebuttal, adding an expandable thumbnail of the UNEP BC graphic in the middle left, using the graphic itself to justify the indented quote.

Hope that was OK.



Soot and global warming

The skeptic argument...

It's soot
"The Intergovernmental Panel On Climate Change (IPCC) drastically understates the warming potential of soot (black carbon) in its report to policy makers. The IPCC has an agenda and that agenda is to blame manmade carbon dioxide emission for climate change. Europe and Asia emit most of the soot from burning coal, wood, dung, and diesel in open fires or without particulate filters in stoves, chimneys, smokestacks, and exhaust pipes. The United States has been restricting soot emissions in Draconian fashion since the Clean Air Act of 1963. The IPCC agenda is really about blaming the United States." (Uncommon Descent)

What the science says...

Soot stays in the atmosphere for days to weeks; carbon dioxide causes warming for centuries.

Soot, also called black carbon (BC), contributes to climate warming in two ways. First, black soot particles in the air absorb sunlight and directly heat the surrounding air. Second, soot falling on snow or ice changes those reflecting surfaces into absorbing ones, that is, soot decreases the albedo. Therefore, soot deposits increase the melting rate of snow and ice, including glaciers and the arctic ice.

Black carbon is a “short-term” climate forcer. Over the short term it is an important contributor to warming; so reducing soot will have immediate benefits in slowing warming over the next 40 years, perhaps by 0.1-0.2°C globally. Decreasing black carbon deposits in the arctic may also slow amplification of feedbacks from melting arctic snow and ice.

Black carbon does not accumulate in the atmosphere like CO2. So, reductions in BC have immediate, but not long-term effects on global warming. CO2 is certainly the “biggest control knob” on climate, and climate change cannot be prevented without reducing carbon emissions. Reductions in BC and CO2 and methane and ozone will be necessary to keep global temperatures from rising more than 2°C above preindustrial levels in the next 50 years.

“It is important to emphasize that BC reduction can only help delay and not prevent unprecedented climate changes due to CO2 emissions.” (Ramanathan and Carmichael. Global and regional climate changes due to black carbon. Nature Geoscience (2008) vol. 1 (4) pp. 221-227)

“Short-lived climate forcers – methane, black carbon and ozone – are fundamentally different from longer-lived greenhouse gases, remaining in the atmosphere for only a relatively short time. Deep and immediate carbon dioxide reductions are required to protect long-term climate, as this cannot be achieved by addressing short-lived climate forcers.” (Integrated Assessment of Black Carbon and Tropospheric Ozone; United Nations Environment Programme, http://www.unep.org/dewa/Portals/67/pdf/Black_Carbon.pdf, 2011)

Because of its short lifetime in the atmosphere the effects of BC are most important regionally, especially in South and East Asia. Other hotspots occur in Mexico, Brazil, Peru, and parts of Africa. In Asia, BC contributes to regional heating and disrupts rainfall patterns. BC is of great concern in the Himalayas where it accelerates melting of glaciers, which supply water to millions.

The largest sources of BC are incomplete burning of biomass and unfiltered diesel exhaust. Major reductions could be achieved by replacing traditional cook and heat stoves in developing countries with clean-burning biomass stoves or alternative fuel systems. Installation of filters on diesel vehicles reduces BC. Industrial coke ovens and brick kilns should also be updated to employ newer, cleaner technologies. Finally, open field burning of agricultural waste should be eliminated. These old technologies are primarily used in developing countries.

In the industrialized northern hemisphere, residential wood stoves are the primary source of BC. Emissions from North America and Europe are the major controllable sources of BC to the Arctic, contributing significantly to northern warming and loss of ice.

The major sources of BC (biomass burning for cooking and heating, and diesel engines) are not the biggest sources of CO2 (coal and fossil fuel burning). Therefore, both problems can and must be addressed independently and simultaneously. Immediate reductions in BC can buy a little time as we convert to low carbon energy sources.

There are reasons besides climate change to reduce BC emissions. Black carbon has serious and well documented health effects; worldwide reductions in soot emissions would prevent an estimated 2.4 million premature deaths. Emissions of BC are accompanied by CO, and volatile organic compounds (VOCs), which have additional adverse health effects.


Integrated Assessment of Black Carbon and Tropospheric Ozone: Summary for Decision Makers. United Nations Environment Programme and World Meteorological Organization (2011) pp. 1-36.

Lacis et al. Atmospheric CO2: Principal Control Knob Governing Earth's Temperature. Science (2010) vol. 330 (6002) pp. 356-359.

Ramanathan and Carmichael. Global and regional climate changes due to black carbon. Nature Geoscience (2008) vol. 1 (4) pp. 221-227.

Rebuttal written by Sarah. Last updated on 28 March 2011.

2011-03-31 17:40:11
Andy S


This is great.

At the risk of being pedantic I'd avoid the "Cinders in the Sky" title since BC is not ash and the damage it does is when it is on the ground as well as as the short time it is in the air.

Coincidentally, I had just started reading the draft EPA report  to Congress on Black Carbon. It's a very long (386 pages), very thorough document. More here.

2011-03-31 18:08:01Updated blog post
John Cook


Sarah, pic looks good. I hope it's okay, I moved it to the right, text is more readable that way. Have added it to the schedule.

Many thanks for writing this! This will go into the iPhone app so next time a skeptic brings it up at a public talk, hopefully there'll be someone in the audience with the SkS iphone app and they can provide the answer :-)

2011-04-01 08:47:35
Sarah Green
Thanks again for all the help from experianced bloggers! Sarah
2011-04-01 16:33:30
Ari Jokimäki


It would be good to include links to the papers in the reference section.

2011-04-02 07:54:51
Rob Honeycutt


Ah!  You just gotta love the first commenter on this article.  I guess Sarah struck a nerve.  :-)

2011-04-03 05:43:28
Sarah Green
Makes me feel like I've joined the SK club. I'm glad someone's reading. Sarah